The present invention relates to Helicobacter pylori-colonized Mongolian gerbils usable for (1) screening the therapeutic effect of a drug for Helicobacter pylori which is considered to be the pathogen of gastric ulcer and duodenal ulcer, recurrence thereof, and diseases such as gastric carcinoma, or (2) for the elucidation of pathology in the above-mentioned diseases caused by infection with Helicobacter pylori, and to a method for preparation thereof. The present invention also relates to a medium for isolation of Helicobacter pylori, and further to a method for screening an anti-Helicobacter pylori substances comprising the use thereof.